Rotative gas lift system



Sept. 13, 1966 J. D. BENNETT ETAL 3,272,143

ROTATIVE GAS LIFT SYSTEM Filed Feb. 13, 1964 SIGNAL LINES u u t 1 KICK TO END T0 3RD TO 4TH CONTROLLE WELL WELL WELL H 250 25b 25C 25 TO OTHER m WELLS f4 GAS MANIFOLD FLOW LINES 42 FROM OTHER WELLS (INSTR. GAS) CONTROLLER\ EXHAUST 4s- INTAKE $7 i STORAGE 29 7 3 2 27 3QTTTI 27 x3;

7 4 28- 2 9 SEPARATOR 4s 44 as 34 36% PRODUCTION OUT INVENTORS JOHN D. BENNETT BY JOHN w. PERET ATTORNEY United States Patent 3,272,146 ROTATIVE GAS LlilFT SYSTEM John D. Bennett, Richardson, and John W. Perot, Dallas, Tex., assignors to Sun Oil Company, Philadelphia, Pa, a corporation of New Jersey Filed Feb. 13, 1964, Ser. No. 344,704 21 Claims. (Cl. 103-232) This invention relates to a gas lift system of the rotative type, wherein a plurality of producing wells in a lease are kicked (by feeding compressed gas into their casing-tubing annuli) in a regular sequence, from a single common s urce of compressed gas. The purpose of this kickin of each individual well, of course, is to cause the gas to enter into the tubing of the well and force the well fluids to the surface, i.e., to gas lift the well.

In prior, conventional rotative type gas lift systems, the various wells are kicked or programmed on a time basis, as controlled by a clock at each individual well. This means that it is possible for two wells to be kicked at the same time; as a result, at such times a large amount of gas is suddenly fed to the compressor, this peak load being more than the compressor can handle. Therefore, a very large compressor must be provided (which is uneconomic), or else a very large amount of intake storage (above-ground gas storage) must be provided (which is also uneconomic).

Also, in conventional gas lift arrangements, the lifting gas which follows the slug of liquid out of the well (i.e., the so-oalled tailing gas) is suddenly released to the intake of the compressor, at a rate beyond the handling capability of the compressor. This again calls for a large amount of above-ground gas storage, to avoid popping of the gas (and its consequent loss to the atmosphere) as a result of the buildup of excessive pressure in the storage container.

In conventional gas lift arrangements, the back pressure on the gas lift is maintained quite high, because of the comparatively small-diameter flowline which extends the entire distance between the well and the separator. Since the size of the slug of liquid lifted from the well depends upon the differential pressure (i.e., the difference between the forward or injected pressure and the pressure at the upper end of the tubing, or the back pressure), the high back pressure in conventional arrangements limits the differential pressure and thus limits the size of the slug.

An object of this invention is to provide a novel rotative gas lift system.

Another object is to provide a rotative gas lift system in which the wells are kicked or programmed on such a basis that it is impossible for two wells to be kicked at the same time; thus, the amount of above-ground gas storage which is necessary is reduced as compared to a conventional system, without the necessity of increasing the size of the compressor.

A further object is to provide a rotative gas lift system which operates to slow down the release of tailing gas to the compressor, to a rate which the compressor can handle; thus, the amount of above-ground storage can be reduced, as compared to a conventional system.

A still further object is to provide a gas lift arrangement wherein the back pressure on the gas lift is reduced as compared to a conventional arrangement.

The objects of this invention are accomplished, briefly, in the following manner: In a rotative gas lift system, the wells are kicked or programmed in a prearranged order depending on the output of the compressor, this programming taking place in response to the pressure in the gas manifold (connected to the various wells) as ice built up by the compressor. A separate relatively large expansion chamber is connected to the tubing of each respective well, the flow from each well into its corresponding expansion chamber t-aking place through an on-off valve which is controlled in response to the pressure in the respective chamber. A separate bypass loop, in which there is a flow restrictor, is connected around each respective on-off valve.

A detailed description of the invention follows, taken in conjunction with the accompanying drawing, wherein the single figure is a diagrammatic representation of a rotative gas lift system according to the invention.

Now referring to the drawing, a compressor 1, which is driven continuously by a suitable driving means such as an electric mot-or, compresses the intake gas which it receives from a small surge tank 2 labeled Intake Storage, and delivers or discharges the compressed gas through a pipe 3 to a discharge gas manifold 4, which in its simplest form may be merely a chamber. From manifold 4, a line or pipe 5 can convey the pressured gas (compressed gas) through an on-off valve 6 to the casing-tubing annulus 7 of a well 8, which may be considered as the first well in a rotative gas lift system. From manifold 4, other lines or pipes (one of which is shown at 9) can convey the pressured gas through respective on-oif valves (each of which is similar to valve 6) to the casing-tubing annuli of other wells (the second, third, fourth, etc. wells) in the gas lift system.

The valve 6 is pneumatically operated by means of a diaphragm actuator schematically indicated at 10, in on-off fashion, to selectively open or close the coupling or conduit between manifold 4 and the annulus 7 of well 8. A kick controller 1 1 receives instrumentation gas from line 5 by way of a conduit 12 (which is coupled to line 5 on the manifold side of valve 6), and applies this gas to diaphragm 10 in order to pneumaticaly control the opening and closing of valve 6. When controller 11 is energized :by a suitable electrical voltage, it functions to cause the opening of valve 6; when this voltage is removed from controller 11, the latter functions to cause valve 6 to close. It may be seen that when valve 6 is open, annulus 7 of well 8 is coupled to manifold 4; when valve 6 is closed, well 8 is cut off or decoupled from manifold 4.

Similar kick controllers and pneumatically-operated valves are used for the other wells in the rotative gas lift system, there being a separate controller and valve for each respective well in the system. When each controller is energized, the corresponding valve is opened to couple the manifold 4 to the associated well; when the controller is deenergized, the corresponding valve is closed to cut off the manifold from the respective Well.

A stepping switch 16 is stepped around or operated by a pressure-responsive means 1 4 which is actuated by pressure fluctuations in the compressor discharge manifold 4. A compression spring 15, one end of which bears against a fixed support and the opposite end of which bears against the upper end of an actuating rod 16, tends to urge this rod downward. The upper end of a bellows 17 is connected to the lower end of rod 16, and the interior of bellows 17 is coupled by means of a tube 18 to the interior of manifold 4; when the pressure in manifold 4 increases, this pressure is transmitted to the interior of bellows 17 which then tends to urge rod 16 upward, against the bias of spring 15. A spring-pressed pawl 1-9 is pivotally mounted on rod 16 to engage and drive a ratchet wheel 20 secured to one end of a shaft 21. When rod 16 moves downward, pawl 19 moves down and hooks under the next adjacent tooth on wheel 20; thereafter, when rod 16 moves upward, ratchet wheel 20 is rotated to rotate shaft 21.

The movable contact 22 of stepping switch 13 is secured to the other end of shaft 21, this movable contact engaging individual ones of the fixed contacts 23a, 23b, 23c, 23d, etc. (a total of six fixed contacts are illustrated) in succession as it is stepped around by wheel 20 driving shaft 21. Contact 22 is shown in engagement with fixed contact 23a.

One terminal of a battery 24 is connected to movable contact 22, while the opposite battery terminal is grounded. A signal line 25a is connected between controller 11 of the first well 8 and stepping switch contact 23a, the circuit to battery 24 being completed by means of a ground connection 26 at the controller. Thus, when stepping switch 13 is in the position shown, an energizing voltage is applied to controller 11, thereby to cause opening of valve 6 in the manner previously described.

Similar signal lines 25b, 25c, and 25d are connected between the kick controllers of the second, third, and fourth wells, respectively, and the respective stepping switch contacts 23b, 23c, and 230.. Thus, as stepping switch 13 steps around, energizing voltages are applied to the respective kick controllers for the wells, one at a time and in succession.

A plurality of gas lift valves 27 (illustrated as four in number) are mounted on the tubing 28 of well 8, and similarly in each of the other wells of the rotative gas lift system. These valves are operated by pressures in the annulus 7, and cause the annulus 7 to communicate with the tubing 28 when they open. The valves 27 are shown schematically, as they are of conventional construction. The tubing 28 fills to a certain level with petroleum fluids. When using gas lift valves, pressure is applied to the casing-tubing annulus 7 for gas lift purposes; when the pressure builds up to a certain value, the gas lift valves 27 open, and a slug 29 of liquid starts up the tubing, being pushed up by the so-called lifting gas or tailing gas at 30.

The upper end of tubing 28 communicates by way of a pipe 31, in which is inserted an on-off valve 32, with one end of a chamber 33. Chamber 33 is larger in volume than the slug 29, is located closely adjacent the well 8, and may be made, for example, of two joints of easing, tilted in such a way that the lower end of the chamber is connected to the flowline 34 which leads to the gas-liquid separator 35. Each of the wells of the rotative gas lift system is arranged similarly, each well having a respective pipe similar to 31, a valve similar to 32, a chamber similar to 33, and a flowline similar to 34. The flowline from each well leads from its respective chamber to the single separator 35 which is common to all of the wells; one of these latter fiowlines is indicated at 34'. The wells may be located rather remotely from the separator, e.g. in some cases a mile or two from the separator.

From the separator, produced liquids are taken off via pipe 36, and the gases are fed into the intake storage 2, for re-use by compressor 1, via pipe 37. A pop-off device (pressure relief valve) 38 is coupled to separator 35, for relieving excessive pressures to sales or the atmosphere.

The valve 32 is pneumatically operated by means of a diaphragm actuator schematically indicated at 39, in on-otI fashion, from a pressure-responsive controller 40. Controller 40 is made responsive to the pressure in chamber 33 by means of a pipe 41 coupling the interior chamber 33 to such controller. Controller 40 receives instrumentation gas from line by way of a conduit 42 (which is coupled to line 5 on the manifold side of valve 6), and applies this gas to diaphragm 39 in order to pneumatically control the opening and closing of valve 32. The instrumentation gas is exhausted back into chamber 33 via a pipe 43. When the pressure in chamber 33 rises to a certain value, controller 40 functions to admit instrumentation gas to diaphragm 39, closing valve 32. When the pressure in chamber 33 subsequently decreases, controller 40 causes the instrument control gas to be exhausted from actuator 39 via line 43, reopening valve 32.

Each of the valves 32 (it being remembered that each of the wells in the rotative gas lift system is provided with a respective valve 32) has a bypass pipe loop therearound, in which is located a restricting valve (throttle valve) 44 provided with a manual adjustment means 45 for adjusting or presetting the effective opening provided by this valve.

The operation of the system of this invention will now be explained. Assume that stepping switch 13 has stepped to the position illustrated, wherein contact 22 is in engagement with contact 23a. An energizing voltage is fed to kick controller 11, which then allows gas in line 5 to actuate (open) valve 6. This allows the gas pressure in manifold 4 to enter annulus 7 of well 8. When this takes place, the pressure in manifold 4 decreases or drops, decreasing the pressure in bellows 17 and allowing the spring 15 to rush rod 16 down, lowering pawl 19 so that it rehooks under the next adjacent tooth (in the counterclockwise direction) of ratchet wheel 20.

As the pressure builds up in annulus 7, due to the continued operation of the compressor 1, the gas lift valves 27 open in the conventional manner (that is to say, the well kick), causing the slug 29 to start up the tubing 28. The slug pushes the gas ahead of it (which gas is in the tubing space 46) upwardly. This gas passes unrestricted through valve 32 and int-o chamber 33. (It is pointed out that valve 32 is open at this time because the pressure in chamber 33 is relatively low.) Due to the provision of this chamber, in which the pressure is now relatively low, the back pressure on the gas lift is reduced, so that the size of the slug 29 raised from the well is greatly increased.

The gas ahead of slug 29 passes from the chamber 33 through flowline 34 into separator 35, on into intake storare 2 and to compressor 1, then back into gas manifold 4. As the pressure rises in manifold 4, the bellows 17 moves rod 16 upwardly against spring 15, with the result that pawl 19 rotates ratchet wheel 20, stepping switch 13 around so that contact 22 engages contact 23b. The kick controller for the second well to be gas lifted is now energized, to allow the gas pressure to enter the casing-tubing annulus of this second well, a similar operation to the foregoing then occurring with this second well. When contact 22 leaves contact 23a on its way to contact 23b, controller 11 is tie-energized and valve 6 closes.

The slug 29 reaches chamber 33 at high velocity. As the slug enters the flowline 34, it encounters a restriction to flow, due to the difference in density of the gas (which is ahead of the slug) and the liquid. Then, the pressure in chamber 33 will suddenly rise, caused by the sudden expansion of the tailing gas 30 (some of which has by this time reached chamber 33) against the substantially incompressible liquid of the slug which is (as just stated) restricted in its flow out of chamber 33. As previously described, chamber 33 is larger in volume than the slug 29, so some of this tailing gas can at this time enter chamber 33 and expand therein. This build-up of pressure in chamber 33 will cause the pressure-responsive controller 40 to admit instrument control gas to valve actuator 39, thereby closing valve 32. This effectively cuts off the remaining tailing gas 30 in the well 8; this gas will have to be released from the well through the controlled loop or bypass line including restricting or throttle valve 44. Thus, the release of the tailing gas is slowed to a rate such that the compressor 1 can handle it, without the necessity for large above-ground storage or for (alternatively) popping it to the atmosphere.

The tailing gas 30 will remain behind the slug 29; the energy from the expansion of this tailing gas will push the liquid on into the separator, through flowline 34.

As previously stated, the chamber 33 is located closely adjacent the well 8. By having this chamber so located, it is not necessary to have to push the slug the entire disstance from the well to the separator (which in some cases may be a mile or two) at the same (high) velocity that is required to raise the slug from the well. There is an optimum rate at which the slug should be raised from the well, in order to eliminate the fall back or knifing through. However, once the slug has been removed from the well, it can be moved to the separator 35 at a slower rate and a reduced pressure, using the energy of expansion of the initial volume of tailing gas.

It is pointed out that in the system of this invention the gas is used in one well, then pumped out of that well and put into the next well, and so on, moving around the group of wells in order. Wells that have to be kicked more often than the others can be kicked as often as necessary, as long as the kicks are alternated with other wells. This can be done by appropriate programming in stepping switch 13. If necessary, time delays can be built into the kick controllers such as 11, to make sure that each control valve 6 closes before the next one opens.

It may be noted that the wells are kicked in a prearranged order by a programmer operated by the pressure of the gas supply used for lifting, that is, the wells are programmed on the basis of the capacity or output of the compressor 1. If the wells need be kicked more often, the compressor is slowed down. If the compressor cannot program the frequency at which the wells are to be kicked, a larger compressor should be installed. Due to the fact that the wells are programmed on the capacity of the compressor, rather than on a time basis, the excess amount of gas that would otherwise accumulate from time to time (due to two wells being kicked at the same time) will be eliminated, and the compressor will be able to handle the total gas volume without having a peak load suddenly fall on it. Therefore, the amount of aboveground gas storage which is necessary is reduced.

It is possible that, with the present system, the formation may be under gas pressure for a longer period of time, but it is also true that the size of the slug 29 raised from the well is greatly increased, and the amount of gas pressure necessary to raise the slug is lowered. The amount of gas in the entire system is lowered.

It is pointed out that, instead of being obtained from a compressor, the gas supply used for lifting may be obtained from a high-pressure gas well. In this case, the gas discharge pipe 37 of the separator could go to sales, instead of to intake storage 2.

Although the controller 40 has been described as being responsive to the pressure in chamber 33, it could, in the alternative, be arranged to be responsive to mass rate of flow or to volume. However, it is preferably pressureresponsive, as described.

The invention claimed is:

1. In a rotative gas lift system, a plurality of wells each having therein gas lift devices to which compressed gas may be supplied to lift well fluids to the surface; a single source of compressed gas, a separate coupling between the gas lift devices of each respective well and said source, a separate control valve in each respective coupling, and means responsive to variations in pressure of said source for causing the opening of said control valves one at a time and in a predetermined sequence, the arrangement being such that each respective control valve is closed prior to the opening of the valve immediately following in the sequence.

2. System in accordance with claim 1, wherein said means causes the opening of each control valve in response to an increase in the pressure of said source.

3. System as defined in claim 1, wherein said source comprises a gas manifold fed by a compressor receptive of gas derived from the tubing strings of the wells.

4. System in accordance with claim 1, wherein said means causes the closing of each control valve in response to a decrease in the pressure of said source followed by an increase in such pressure.

5. In combination, a well having therein a string of tubing with which are associated gas lift devices to which compressed gas may be supplied to lift a slug of well fluids to the surface through said tubing; a chamber positioned closely adjacent said well and having its inlet coupled to the upper end of said tubing, said chamber having a volume in excess of the expected volume of said slug; a gas-liquid separator remote from said well, means coupling the outlet of said chamber to said separator, and means for supplying compressed gas to said lift devices.

6. Combination as defined in claim 5, wherein said last-mentioned means operates to supply compressed gas to said devices repetitively, at spaced intervals.

7. Combination as defined in claim 5, wherein the coupling between the upper end of the tubing and the inlet of said chamber is controllable to vary the fluid transmission characteristics of such coupling.

8. In combination, a well having therein a string of tubing with which are associated gas lift devices to which compressed gas may be supplied to lift a slug of well fluids to the surface through said tubing; a chamber positioned closely adjacent said well and having its inlet coupled to the upper end of said tubing, said chamber having a volume in excess of the expected volume of said slug; a gas-liquid separator remote from said well, means coupling the outlet of said chamber to said separator,

a source of compressed gas, a controllable coupling between said source and said devices, and means responsive to variations in pressure of said source for controlling said coupling.

9. Combination as defined in claim 8, wherein said last-mentioned means is constructed and arranged to control said coupling repetitively, at spaced intervals.

10. Combination as defined in claim 8, wherein said last-mentioned means is constructed and arranged to repetitively and at spaced intervals render said coupling effective, thereby to supply compressed gas to said devices.

11. Combination as defined in claim 8, wherein the coupling between the upper end of the tubing and the inlet of said chamber is controllable to vary the fluid transmission characteristics of such coupling.

12. In a rotative gas lift system, a plurality of wells each having therein a string of tubing with which are associated gas lift devices 'to which compressed gas may be supplied to lift a slug of well fluids to the surface through the respective tubing string; a separate chamber positioned closely adjacent each respective one of said wells, each chamber being coupled to the upper end of the tubing of its corresponding well, each chamber having a volume in excess of the expected volume of the corresponding slug; a single source of compressed gas, a separate coupling between the gas lift devices of each respective well and said source, a separate control valve in each respective coupling, and means responsive to variation-s in pressure of said source for causing the opening of said control valves one at a time and in a predetermined sequence.

13. System as defined in claim 12, wherein said source comprises a gas manifold fed by a compressor receptive of gas derived from the tubing strings of the wells.

14. System as defined in claim 12, wherein each of the couplings between the upper end of a tubing string and the corresponding chamber is controllable to vary the fluid transmission characteristics of the respective coupling.

15. System as recited in claim 14, including also separate control means coupled to each respective chamber, and responsive to the pressure in the corresponding chamber, for controlling the associated coupling.

16. In combination, a well having therein a string of tubing with which are associated gas lift devices to which compressed gas may be supplied to lift a slug of well fluids to the surface through said tubing; a chamber positioned closely adjacent said well, said chamber having a volume in excess of the expected volume of said slug; a controllable coupling between the upper end of said tubing and said chamber, control means coupled to said chamher, and responsive to the pressure therein, for controlling said coupling, and means for supplying compressed gas to said lift devices.

17. Combination in accordance with claim 16, wherein said controlling means decreases the effective cross-section of said coupling in response to an increase of the pressure in said chamber.

18. In combination, a well having therein a string of tubing with which are associated gas lift devices to which compressed gas may be supplied to lift a slug of well fluids to the surface through said tubing; a chamber positioned closely adjacent said well and coupled to the upper end of said tubing, said chamber having a volume in excess of the expected volume of said slug; a source of compressed gas, a controllable coupling between said source and said devices, and means responsive to an increase in the pressure of said source for rendering said coupling effective, thereby to supply compressed gas to said devices.

19. In combination, a well having therein a string of tubing with which are associated gas lift devices to which compressed gas may be supplied to lift a slug of well fluids to the surface through said tubing; a chamber positioned closely adjacent said well and coupled to the upper end of said tubing, said chamber having a volume in excess of the expected volume of said slug; a source of compressed gas, a controllable coupling between said source and said devices, and means responsive to a decrease in the pressure of said source, followed by an increase in such pressure, for rendering said coupling ineffective.

20. In combination, a well having therein a string of tubing with which are associated gas lift devices to which compressed gas may be supplied to lift a slug of well fluids to the surface through said tubing; a chamber positioned closely adjacent said well, said chamber having a volume in excess of the expected volume of said slug; a controllable coupling between the upper end of said tubing and said chamber, control means coupled to said chamber, and responsive to the pressure therein, for controlling said coupling, a source of compressed gas, a controllable coupling between said source and said devices, and means responsive to variations in the pressure of said source for controlling said last-mentioned coupling.

21. Combination in accordance with claim 20, wherein said control means decreases the effective cross-section of said first-mentioned coupling in response to an increase of the pressure in said chamber.

References Cited by the Examiner UNITED STATES PATENTS 2,275,947 3/1942 Courtney l03232 2,947,318 8/1960 Odom 137-624.18 2,975,724 3/1961 Welchon l03233 3,152,611 10/1964 Hubby 137624.l4 3,191,681 6/1965 Hubby 137-62418 MARK NEWMAN, Primary Examiner.

W. J. KRAUSS, Assistant Examiner. 

1. IN A ROTATIVE GAS LIFT SYSTEM, A PLURALITY OF WELLS EACH HAVING THEREIN GAS LIFT DEVICES TO WHICH COMPRESSED GAS MAY BE SUPPLIED LIFT WELL FLUIDS TO THE SURFACE; A SINGLE SOURCE OF COMPRESSED GAS, A SEPARATE COUPLING BETWEEN THE GAS LIFT DEVICES OF EACH RESPECTIVE WELL AND SAID SOURCE, A SEPARATE CONTROL VALVE IN EACH RESPECTIVE COUPLING, AND MEANS RESPONSIVE TO VARIATIONS IN PRESSURE OF SAID SOURCE FOR CAUSING THE OPENING OF SAID CONTROL VALVES ONE AT A TIME AND IN A PREDETERMINED SEQUENCE, THE ARRANGEMENT BEING SUCH THAT EACH RESPECTIVE CONTROL VALVE IS CLOSED PRIOR TO THE OPENING OF THE VALVE IMMEDIATELY FOLLOWING IN THE SEQUENCE. 